1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device with a digitizer and a method for manufacturing the same.
2. Discussion of the Related Art
The resolution of a liquid crystal display (hereinafter, referred to as “LCDs”) has been rapidly increased by the improvements in liquid crystal materials and micro fabrication technology with characteristics of lightweight, filed emission display and low power consumption. Also, the range of applications in which LCDs are used is becoming broader. As an example, the LCD is used as a display device of a notebook personal computer (hereinafter, referred to as “NTPC”.) The NTPC is slim and lightweight. A liquid crystal module (hereinafter, referred to as “LCM”) used in various video display devices including a backlight unit and a liquid display panel, will be explained.
FIG. 1 is an exploded view of a general liquid crystal display module LCM 10. As shown in FIG. 1, the LCM 10 includes a backlight 12 and an LCD panel 11. The backlight 12 and the LCD panel 11 are supported by a main support 13 and a top case 20. A reflecting plate 12a, a light-guiding plate 12b, a first diffusing or protecting sheet 12c, a first prism sheet 12d, a second prism sheet 12e and a second diffusing or protecting sheet 12f are stacked up in that order on top of the main support 13. Meanwhile, an upper side of the LCD panel 11 is connected to the top case 20 of the metal material, and a lower side of the LCD panel is supported by the main support 13. The backlight, including the reflecting plate 12a, the light-guiding plate 12b and the sheets, is a lower unit underneath the LCM 10 for uniformly irradiating light to the LCD panel.
Recently, high resolution of LCD devices has been realized as a result of great improvements in LCD technology, making LCDs useful in high resolution graphics work. In addition, a digitizer is used as an input device in a computer having the aforementioned LCD device as well. The digitizer of the LCD device is classified into a resistive type, electrostatic capacitance type and EM (electro-magnetic) type according to the method of determining a user-indicated location.
The resistive type senses a location being pressed by determining pressure through a change of an amount of an electric current in a the direct current voltage that is obtained. The electrostatic capacitance type senses the pressed location by using capacitance coupling in an alternating current voltage signal that is obtained. The electro-magnetic type senses the pressed location by detecting a resonance frequency in a magnetic field that is obtained. Each type has different characteristics of signal amplification problems, different resolutions and a different degree of difficulty of design and technology. The type of digitizer used depends on the precision, based on optical, electrical, mechanical, size, and input characteristics as well as endurance and economical efficiency.
The design and structure of the EM type digitizer merits closer scrutiny for its ability to discriminate an exact location better than the other types of digitizers. The EM type digitizer includes a digitizer having two sets of array coils, one set of which is parallel to the other set, and an electronic (stylus). The EM type digitizer may be formed at the rear of the backlight of the aforementioned LCD device.
FIG. 2 is a block diagram illustrating a driving circuit and a driving method of an EM type digitizer according to the related art. Referring to FIG. 2, the digitizer includes a digitizer plate 40, a controller 15, and an electronic (stylus) pen 39. At this time, the digitizer plate 40 serves as a sensor detecting a touching point by transmitting and receiving an electromagnetic wave resonated in the touching point, and the controller 15 controls the digitizer plate. Also, the electronic pen 39 communicates with the digitizer plate 40 by transmitting and receiving electromagnetic waves.
Furthermore, the digitizer plate 40 (hereinafter, referred to as ‘digitizer’) includes a sensor PCB having a plurality of X-axis and Y-axis coils, a shield plate (not shown) blocking the electromagnetic wave at a bottom of the sensor PCB and a connector having a switching means for directing transmitting and receiving modes of the sensor PCB and selecting the X or Y axis coils. The controller 15 positioned at the bottom of the digitizer 40 includes a CPU (control processor unit) sending a signal to the digitizer and reading the input signal so as to detect the location of the electronic pen 39. The electronic pen 39 includes a resonance circuit having there in a coil and a condenser.
The structure of the digitizer 40 will be described as follows. The digitizer 40 includes X-axis and Y-axis coil arrays and X-MUX and Y-MUX coupled to the X-axis and Y-axis, respectively. A specified Y-axis coil is selected by a Y address signal (Y-ADDR), a specified X-axis coil is selected by an X address signal (X-ADDR) for reading. Both X and Y address signals are generated from the controller 15.
A sine wave and an electromagnetic wave are sent to X-axis and Y-axis by the controller 15 and the output signal from the X-axis and Y-axis coil is sent to the controller 15. The controller 15 includes a sine wave generator 31 generating the sine wave and sending it to the coils, an amplifier 32 amplifying the sine wave generated from the sine wave generator 31, a switch 30 sending the sine wave amplified from the amplifier 32 to the coil or sending a signal from the coil to the controller 15, an amplifier 34 grading and amplifying an output signal generated from the coil by the switch 30, a wave detector 35 detecting waves from output of the amplifier 34, a low pass filter 36 filtering the signal generated from the wave detector 35, a sample and hold unit 37 (S/H) sampling, holding and outputting a signal generated from the low pass filter 36, an analog-digital converter 38 converting the size and polarity of an analog signal outputted from the sample and hold unit 37 to a digital format and outputting the digital signal, and a processor 33 reading the output signals from the analog-digital converter 38 for finding the location of the electronic pen 39 and controlling all other units. While the analog-digital converter 38 is digitizing, the sample and hold unit 37 holds a measured value of a coil and a second following coil measurement is started at a front circuit.
The digitizer 40 includes a plurality of coils being piled up on a flexible surface of the PCB. Each coil is arrayed against X-axis and Y-axis, and has a first side being connected to a grounding voltage and a second side being connected to a mux unit in which one coil is chosen to be connected to an electric potential line of a fixed level.
The operation of the electromagnetic induction touch panel is as follows. The sine wave generated from the sine wave generator 31 by the processor 33 is transmitted to the sensor unit 29 through the amplifier 32 and the switch 30. The sensor unit 29 selects an X-axis coil and a Y-axis coil so as to generate electromagnetic waves by inducing an electromagnetism. The electronic pen 39 is resonated, the resonant frequency is held for a predetermined time and the sensor unit 29 receives the electromagnetic waves generated from the electronic pen 39.
The electric pen 39 includes the resonance circuit. The resonance circuit is an RLC complex circuit in which a maximum electric current flows at a specified frequency of an approved power. The resonant frequency can abstract output characteristics of a specified resonant frequency. The resonant frequency (f) is expressed as a mathematic formula as   f  =      1          2      ⁢      π      ⁢              LC            (here, L is an inductance of a coil and C is a capacity of the condenser.) According to the electronic pen 39, each sine wave voltage in different sizes is induced to each coil arrayed in the sensor unit 29 and inputted into the processor 33 through the wave detector and the analog-digital converter 38.
The processor 33 calculates the value of the position of the electronic pen 39 on the digitizer 40 from the value induced to a coil and outputs the angle value between 0° and 360°. The output data of the electronic pen 39 is induced to the liquid crystal display panel or stored in the processor 33.
It is more convenient for a user to draw a figure when an area of the electromagnetic digitizer is larger and it is more efficient when the resolution is higher. The resolution is inversely proportional to the space between coils in the digitizer 40. That is, when the spaces between the coils are narrower, the resolution becomes higher. The electromagnetic touch panel using a totally different method from the resistant film type detects an exact location of the electronic pen by using a characteristic of an electromagnetic field being induced and being resonated. The electromagnetic touch panel uses a stable way for not affecting image quality and includes the sensor unit and the controller at the rear of a display device so as to maintain the high transmittance of the display device. The electromagnetic touch panel is not affected by hand touch but only by the pen, and the writing is as natural as handwriting. Therefore, it can be used in graphic design, or in business.
In the EM type, a plurality of coils are provided inside the digitizer 40, so that it is possible to detect the touching point of the electron pen 39 by detecting electric field changes. Accordingly, unlike the resistive type, mounting the digitizer at the front of the LCD panel is not required as it is in the EL type. That is, the digitizer of the EM type may be mounted at the rear of the LCM 10. In case the LCM 10 having electromagnetic connection characteristics is formed, it is possible to detect the touching point of the electron pen even though the digitizer 40 is positioned below the LCM 10.
FIG. 3 schematically illustrates the digitizer mounted at the rear of the LCM. In general, a printed circuit board (hereinafter, referred to as PCB) is provided at the bottom of the main support at the rear of the LCD device. A drive integrated circuit (hereinafter, referred to as D-IC) for driving switching devices (TFT array) of the LCM 10 is provided on the PCB. And, the LCM 10 and the PCB 45 having the D-IC are electrically connected by a tape carrier package 14 (hereinafter, referred to as TCP) so as to send a control signal of the D-ICs (a gate line driving signal) and a video signal (a data line driving signal) to each gate and data line of the LCD panel. Although there is minor variation among products, a PCB 45a having a drive IC for driving the data line is connected to the TCP 14 at a corner in a long-axis direction of the LCD panel and the PCB 45b having the drive IC for driving the gate line at a corner in a short-axis direction of the LCD panel.
Accordingly, the LCM is driven by a control signal and a video signal of the D-IC provided at the PCB 45, and changes the structure of the arrangement of liquid crystals to display picture corresponding to the video signal by a light channel formed according to the arrangement of liquid crystals on the liquid crystal display device. Therefore, when the digitizer is provided at the rear of the LCM, it is desirable that the electro-magnetically uniform LCM is arrayed on a top surface of the digitizer and materials that are not electro-magnetically uniform such as the PCB are provided on a lower surface of the digitizer.
An assembling method for an LCD device having an EM type digitizer as described in FIG. 3 includes inserting the digitizer between the main support 13 and the PCB 45 after the LCM 10 is assembled. When inserting the digitizer, as shown in FIG. 3, the digitizer should be lifted upward and fixed into place to reduce a damage to the TCP 14 when electrically connecting the PCB 45 to the LCD panel 10.
However, there are a number of problems in lifting the PCB 45 and fixing the digitizer as follows. First, when the digitizer 40 is fixed, the inserted digitizer, the PCB 45 and the TCP 14 are contacted and damaged, reducing quality. Also, when the PCB 45 and the TCP 14 are lifted to insert the digitizer, the TCP 14 connected to the PCB 45 is contacted with the top case 20 and is easily cracked. Particularly, the quality and manufacturing yield are reduced when the PCB 45 are provided at both corners of the long and short axis direction of the liquid crystal display panel. Furthermore, in the case where an end of the top case 20 has a burr having a kinked end the damage of the TCP is accelerated.
Second, the PCB that is screwed into place left a predetermined space remaining between the main support and the PCB so as to allow insertion of the digitizer according to the related art devices art. But the size of the LCD had to be large to accommodate this extra space such that the digitizer was not provided in an LCD that was lightweight and slim.
Therefore, when the digitizer was inserted between the LCM and PCB, there was a problem that PCB had to be lifted and the PCB and the TCP were prone to easy damage. The quality of the devices and the manufacturing yield.